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Abstract:

An imprint lithography template includes a porous material defining a
multiplicity of pores with an average pore size of at least about 0.4 nm.
The porous material includes silicon and oxygen, and a ratio of Young's
modulus (E) to relative density of the porous material with respect to
fused silica (pporous/pfused silica) is at least about 10:1. A
refractive index of the porous material is between about 1.4 and 1.5. The
porous material may form an intermediate layer or a cap layer of an
imprint lithography template. The template may include a pore seal layer
between a porous layer and a cap layer, or a pore seal layer on top of a
cap layer.

Claims:

1. A imprint lithography template comprising:a porous material defining a
multiplicity of pores with an average pore size of at least about 0.4 nm,
whereinthe porous material comprises silicon and oxygen,a refractive
index of the porous material is between about 1.4 and about 1.5, anda
ratio of Young's modulus (E, GPa) to relative density of the porous
material with respect to fused silica (pporous/pfused silica)
is at least about 10:1.

2. The imprint lithography template of claim 1, wherein the Young's
modulus of the porous material is at least about 10 GPa.

3. The imprint lithography template of claim 1, wherein the relative
density of the porous material with respect to fused silica is at least
about 50%.

9. The imprint lithography template of claim 6, further comprising a seal
layer adhered to the cap layer, wherein the seal layer is permeable to
helium gas in contact with the seal layer and substantially impermeable
to species larger than helium.

10. The imprint lithography template of claim 9, wherein the seal layer is
positioned between the porous layer and the cap layer.

11. The imprint lithography template of claim 9, wherein a thickness of
the seal layer is less than about 10 nm.

12. A method of forming an imprint lithography template, the method
comprising:forming a layer of porous material on a surface of an imprint
lithography template, the porous layer defining a multiplicity of pores
with an average pore size of at least about 0.4 nm, wherein:the porous
material comprises oxygen and silicon,a refractive index of the porous
material is between about 1.4 and about 1.5, anda ratio of Young's
modulus (E, GPa) to relative density of the porous material with respect
to fused silica (pporous/pfused silica) is at least about 10:1.

13. The method of claim 12, further comprising forming a second layer on
the porous layer.

14. The method of claim 12, further comprising etching the porous layer.

16. The method of claim 12, further comprising forming an etch stop layer
between the surface of the imprint lithography template and the porous
layer.

17. The method of claim 12, further comprising forming a seal layer on the
surface of the porous layer.

18. The method of claim 17, further comprising forming a cap layer on a
surface of the seal layer.

19. The method of claim 12, further comprising forming a marker region
between the surface of the imprint lithography template and the porous
layer.

20. The method of claim 12, further comprising chemical-mechanical
planarization of the porous layer.

21. The method of claim 12, wherein the porosity of the porous layer is
non-uniform.

22. A method of forming a layer on an imprint lithography template, the
method comprising:positioning an imprint lithography template defining a
multiplicity of pores in a vacuum chamber;evacuating the chamber a first
time;purging the chamber with a first inert gas;evacuating the chamber a
second time;saturating the chamber and the imprint lithography template
with a second inert gas;introducing a silicon-containing gas and one or
more other gases into the chamber; andinitiating a plasma process to
deposit a silicon-containing layer on the surface of the imprint
lithography template.

23. An imprint lithography template comprising:a first layer;a second
layer, wherein the second layer is a patterned layer of an imprint
lithography template; andtwo or more intermediate layers positioned
between the first layer and the second layer, wherein at least one of the
intermediate layers is a porous layer and at least one of the
intermediate layers is a stress relief layer configured to reduce a force
acting on the porous intermediate layer.

24. An imprint lithography template comprising:a first layer;a second
layer, wherein the second layer is a patterned layer of an imprint
lithography template; andan intermediate layer positioned between the
first layer and the second layer, wherein the intermediate layer is
configured to reduce a force acting on the patterned second layer.

25. An imprint lithography template comprising:a first layer;a second
layer; andan intermediate layer positioned between the first layer and
the second layer of the imprint lithography template, wherein the
intermediate layer is configured to allow assessment of a thickness of
the second layer based on a difference in physical properties between the
intermediate layer and the second layer.

[0003]Nano-fabrication includes the fabrication of very small structures
that have features on the order of 100 nanometers or smaller. One
application in which nano-fabrication has had a sizeable impact is in the
processing of integrated circuits. The semiconductor processing industry
continues to strive for larger production yields while increasing the
circuits per unit area formed on a substrate; therefore nano-fabrication
becomes increasingly important. Nano-fabrication provides greater process
control while allowing continued reduction of the minimum feature
dimensions of the structures formed. Other areas of development in which
nano-fabrication has been employed include biotechnology, optical
technology, mechanical systems, and the like.

SUMMARY

[0004]In one aspect, an imprint lithography template includes a porous
material defining a multiplicity of pores with an average pore size of at
least about 0.4 nm. The porous material includes silicon and oxygen. A
refractive index of the porous material is between about 1.4 and about
1.5, and a ratio of Young's modulus (E) to relative density of the porous
material with respect to fused silica (pporous/pfused silica)
is at least about 10:1.

[0005]Implementations may include one or more of the following features.
For example, the Young's modulus of the porous material may be at least
about 2 GPa, at least about 5 GPa, at least about 10 GPa, or at least
about 20 GPa. The relative density of the porous material with respect to
fused silica may be at least about 50% or at least about 65%. The porous
material may include SiOxi and 1≦×≦2.5. The
pores may be substantially closed or interconnected. Interconnected pores
may form channels in the porous material.

[0006]In some cases, the template further includes a base layer and a cap
layer, and the porous material forms a layer between the base layer and
the cap layer. The cap layer may be porous. The cap layer may be etched
or patterned such that protrusions extend from a surface of the cap
layer. The base layer may include fused silica. Stress in the porous
material may be neutral to compressive. The porosity of the porous
material, or porous layer, may be non-uniform or asymmetric. The porous
material may have a non-uniform porosity gradient. A non-uniform porous
layer may be achieved by changing one or more parameters during the
formation of a porous layer. The parameter to be changed may be a vapor
deposition process parameter. A vapor deposition process may include
atomic layer deposition. In some cases, an imprint lithography template
may include one or more layers (e.g., an adhesion layer) between the base
layer and the porous layer.

[0007]The porosity of a porous layer (e.g., between a base layer and a cap
layer) may range from about 0.1% to about 60% (e.g., about 1% to about
20%, or about 5% to about 15%). In some cases, the porosity of a porous
layer may be at least about 10%, or at least about 20%. The porosity of a
cap layer may range from about 0.1% to about 20% (e.g., from about 1% to
about 20%, or from about 3% to about 15%).

[0008]The template may further include a seal layer adhered to the cap
layer. The seal layer may be is permeable to helium gas in contact with
the seal layer and substantially impermeable to species larger than
helium. The seal layer may include silicon oxide. The seal layer may be
positioned between the porous layer and the cap layer. The seal layer may
be conformal and/or uniform in thickness. A thickness of the seal layer
may be less than about 10 nm, less than about 5 nm, less than about 3 nm,
or about twice the pore radius. In some cases, the seal layer may be
selected to interact with a mold release agent.

[0009]In another aspect, forming an imprint lithography template includes
forming a layer of porous material on a surface of an imprint lithography
template. The porous layer defines a multiplicity of pores with an
average pore size of at least about 0.4 nm. The porous material includes
oxygen and silicon. A refractive index of the porous material is between
about 1.4 and about 1.5, and a ratio of Young's modulus (E) to relative
density of the porous material with respect to fused silica
(pporous/pfused silica) is at least about 10:1.

[0010]In some implementations, as second layer may be formed on the porous
layer. In some cases, the porous layer may be etched to form a patterned
layer. Forming the porous layer may include etching the porous layer.
Forming the porous layer may include a vapor deposition process, such as
plasma enhanced chemical vapor deposition. The porosity of the porous
layer may be substantially uniform or non-uniform. For example, the
porosity may be asymmetric, or the porosity gradient may be non-uniform,
such that a portion of the layer to be etched is less porous than other
portions of the layer.

[0011]An etch stop layer may be formed between the surface of the imprint
lithography template and the porous layer. A seal layer may be formed on
the surface of the porous layer. A cap layer may be formed on a surface
of the seal layer. Alternatively, a cap layer may be formed on the porous
layer, and a seal layer may be formed on the cap layer. In some cases,
the porous layer is etched to form a patterned layer. A marker region may
be formed between the surface of the imprint lithography template and the
porous layer. The marker region may serve as a thin film optical
metrology marker on the base layer. In some cases, a region of a base
layer may be masked while forming the porous layer to create a recess in
the porous layer form film thickness metrology. In some cases, a porous
layer (e.g., an intermediate porous layer or a porous cap layer) may be
polished, for example, using a chemical-mechanical planarization process.
In some cases, a mesa may be etched in a porous layer or a base layer.

[0012]In another aspect, forming a layer on an imprint lithography
template includes positioning an imprint lithography template defining a
multiplicity of pores in a vacuum chamber, evacuating the chamber a first
time, purging the chamber with a first inert gas, and evacuating the
chamber a second time. The chamber may then be saturated with a second
inert gas. A silicon-containing gas and one or more other gases may be
introduced into the chamber, and a plasma process may be initiated to
deposit a silicon-containing layer on the surface of the imprint
lithography template. This process substantially fills pores in the
porous layer of the imprint lithography template with an inert gas before
the silicon-containing layer is deposited on the porous layer. With the
pores in the porous layer filled with inert gas, reactants used to form
the silicon-containing layer are inhibited from diffusing into the porous
layer and clogging the pores, changing the chemical and physical nature
of the porous layer. Thus, the porous layer remains substantially
uniform, and does not become more dense near the silicon-containing
layer.

[0013]In one aspect, an imprint lithography template includes a first
layer and a second layer. The second layer is a patterned layer of an
imprint lithography template. Two or more intermediate layers are
positioned between the first layer and the second layer. At least one of
the intermediate layers is a porous layer and at least one of the
intermediate layers is a stress relief layer configured to reduce a force
acting on the porous intermediate layer. In another aspect, an imprint
lithography template includes a first layer, a second layer, and an
intermediate layer positioned between the first layer and the second
layer. The second layer is a patterned layer of an imprint lithography
template, and the intermediate layer is configured to reduce a force
acting on the patterned second layer. In another aspect, an imprint
lithography template includes a first layer and one or more layers on the
first layer. At least one of the one or more layers is porous. A stress
relief layer may be positioned on the back side of the template to
counter a force produced by the layer or layers on the first layer.

[0014]In some implementations, the first layer is a base layer and the
second layer is a top layer. The top layer may be a cap layer. The stress
relief layer provides a compressive force, and the compressive force
reduces a tensile force acting on the porous intermediate layer. In other
implementations, the stress relieve layer provides a tensile force, and
the tensile force reduces a compressive force acting on the porous
intermediate layer. In some cases, a neutral to compressive stress state
is maintained in the porous intermediate layer during static and dynamic
conditions, such as template bending during separation.

[0015]The porous intermediate layer may be positioned between two stress
relief layers, the stress relief layer may be positioned between two
porous intermediate layers, or any combination thereof. The stress relief
layer may include a metal, metal oxide, metal nitride, or metal carbide.
In some cases, the stress relief layer is porous (i.e., more porous or
less dense than fused silica).

[0016]In one aspect, an imprint lithography template includes a first
layer, a second layer, and an intermediate layer positioned between the
first layer and the second layer of the imprint lithography template. The
intermediate layer is configured to allow assessment of a thickness of
the second layer based on a difference in physical properties between the
intermediate layer and the second layer.

[0017]In some implementations, the first layer is a base layer and the
second layer is a top layer or a cap layer. The intermediate layer may an
etch stop layer. The intermediate layer may include a metal, metal oxide,
metal carbide, or metal nitride. The intermediate layer may provide
stress relief for the top layer. The physical property may be an optical
property, such as transmittance or reflectance. In some cases, the
intermediate layer is non-continuous. That is, the intermediate layer may
include one or more separate regions (e.g., marker regions). A thickness
of the intermediate layer may be less than about 30 nm, less than about
20 nm, less than about 10 nm, less than about 5 nm, or less than about 3
nm. Thus, the intermediate layer, even if discontinuous, may not
introduce a noticeable perturbation to the second layer. In some cases,
the second lay may be polished to form a substantially smooth surface.
When marker regions are used, the regions may be located outside of the
area occupied by the mesa or patterned portion of an imprint lithography
template.

[0018]Aspects and implementations described herein may be combined in ways
other than described above. Other aspects, features, and advantages will
be apparent from the following detailed description, the drawings, and
the claims.

BRIEF DESCRIPTION OF DRAWINGS

[0019]FIG. 1 illustrates a simplified side view of a lithographic system.

[0020]FIG. 2 illustrates a simplified side view of the substrate shown in
FIG. 1 having a patterned layer positioned thereon.

[0021]FIG. 3 illustrates a side view of a gas pocket trapped between a
substrate and a template.

[0022]FIG. 4 illustrates a side view of a template with a porous layer.

[0036]FIGS. 17A and 17B illustrate a nano-imprint lithography template
with a marker region for use as a metrology marker.

[0037]FIGS. 18A and 18B are photographs that show spreading of imprint
resist between a substrate and a template with a porous intermediate
layer.

[0038]FIGS. 19A, 19B, and 19C are photographs that show spreading of
imprint resist between a substrate and a template without a porous layer.

[0039]FIGS. 20A and 20B are photographs that show rapid wicking of imprint
resist into a porous template.

[0040]FIGS. 21A and 21B are photographs that show slow wicking of imprint
resist into a template with a porous layer and a cap layer.

[0041]FIGS. 22A through 22D are photographs that show filling of voids
between droplets in contact with a template as the droplets spread.

DETAILED DESCRIPTION

[0042]An exemplary nano-fabrication technique in use today is commonly
referred to as imprint lithography. Exemplary imprint lithography
processes are described in detail in numerous publications, such as U.S.
Patent Application Publication No. 2004/0065976, U.S. Patent Application
Publication No. 2004/0065252, and U.S. Pat. No. 6,936,194, all of which
are hereby incorporated by reference herein.

[0043]An imprint lithography technique disclosed in each of the
aforementioned U.S. patent application publications and patent includes
formation of a relief pattern in a formable (polymerizable) layer and
transferring a pattern corresponding to the relief pattern into an
underlying substrate. The substrate may be coupled to a motion stage to
obtain a desired positioning to facilitate the patterning process. The
patterning process uses a template spaced apart from the substrate and
the formable liquid applied between the template and the substrate. The
formable liquid is solidified to form a rigid layer that has a pattern
conforming to a shape of the surface of the template that contacts the
formable liquid. After solidification, the template is separated from the
rigid layer such that the template and the substrate are spaced apart.
The substrate and the solidified layer are then subjected to additional
processes to transfer a relief image into the substrate that corresponds
to the pattern in the solidified layer.

[0044]Referring to FIG. 1, illustrated therein is a lithographic system 10
used to form a relief pattern on substrate 12. An imprint lithography
stack may include substrate 12 and one or more layers (e.g., an adhesion
layer) adhered to the substrate. Substrate 12 may be coupled to substrate
chuck 14. As illustrated, substrate chuck 14 is a vacuum chuck. Substrate
chuck 14, however, may be any chuck including, but not limited to,
vacuum, pin-type, groove-type, electromagnetic, and the like, or any
combination thereof. Exemplary chucks are described in U.S. Pat. No.
6,873,087, which is hereby incorporated by reference herein.

[0045]Substrate 12 and substrate chuck 14 may be further supported by
stage 16. Stage 16 may provide motion about the x-, y-, and z-axes. Stage
16, substrate 12, and substrate chuck 14 may also be positioned on a base
(not shown).

[0046]Spaced-apart from substrate 12 is a template 18. Template 18 may
include a mesa 20 extending therefrom towards substrate 12, mesa 20
having a patterning surface 22 thereon. Further, mesa 20 may be referred
to as mold 20. Template 18 and/or mold 20 may be formed from such
materials including, but not limited to, fused-silica, quartz, silicon,
organic polymers, siloxane polymers, borosilicate glass, fluorocarbon
polymers, metal, hardened sapphire, and the like, or any combination
thereof. As illustrated, patterning surface 22 comprises features defined
by a plurality of spaced-apart recesses 24 and/or protrusions 26, though
embodiments of the present invention are not limited to such
configurations. Patterning surface 22 may define any original pattern
that forms the basis of a pattern to be formed on substrate 12.

[0047]Template 18 may be coupled to chuck 28. Chuck 28 may be configured
as, but not limited to, vacuum, pin-type, groove-type, electromagnetic,
and/or other similar chuck types. Exemplary chucks are further described
in U.S. Pat. No. 6,873,087, which is hereby incorporated by reference
herein. Further, chuck 28 may be coupled to imprint head 30 such that
chuck 28 and/or imprint head 30 may be configured to facilitate movement
of template 18.

[0048]System 10 may further comprise a fluid dispense system 32. Fluid
dispense system 32 may be used to deposit polymerizable material 34 on
substrate 12. Polymerizable material 34 may be positioned upon substrate
12 using techniques such as drop dispense, spin-coating, dip coating,
chemical vapor deposition (CVD), physical vapor deposition (PVD), thin
film deposition, thick film deposition, and the like, or any combination
thereof. Polymerizable material 34 (e.g., imprint resist) may be disposed
upon substrate 12 before and/or after a desired volume is defined between
mold 20 and substrate 12 depending on design considerations.
Polymerizable material 34 may include components as described in U.S.
Pat. No. 7,157,036 and U.S. Patent Application Publication No.
2005/0187339, both of which are hereby incorporated by reference herein.

[0049]Referring to FIGS. 1 and 2, system 10 may further comprise an energy
source 38 coupled to direct energy 40 along path 42. Imprint head 30 and
stage 16 may be configured to position template 18 and substrate 12 in
superimposition with path 42. System 10 may be regulated by a processor
54 in communication with stage 16, imprint head 30, fluid dispense system
32, source 38, or any combination thereof, and may operate on a computer
readable program stored in memory 56.

[0050]Either imprint head 30, stage 16, or both may alter a distance
between mold 20 and substrate 12 to define a desired volume therebetween
that is substantially filled by polymerizable material 34. For example,
imprint head 30 may apply a force to template 18 such that mold 20
contacts polymerizable material 34. After the desired volume is
substantially filled with polymerizable material 34, source 38 produces
energy 40, e.g., broadband ultraviolet radiation, causing polymerizable
material 34 to solidify and/or cross-link conforming to shape of a
surface 44 of substrate 12 and patterning surface 22, defining a
patterned layer 46 on substrate 12. Patterned layer 46 may include a
residual layer 48 and a plurality of features shown as protrusions 50 and
recessions 52, with protrusions 50 having a thickness t1 and
residual layer 48 having a thickness t2.

[0051]The above-described system and process may be further implemented in
imprint lithography processes and systems referred to in U.S. Pat. No.
6,932,934, U.S. Patent Application Publication No. 2004/0124566, U.S.
Patent Application Publication No. 2004/0188381, and U.S. Patent
Application Publication No. 2004/0211754, all of which are hereby
incorporated by reference herein.

[0052]In nano-imprint processes in which polymerizable material is applied
to a substrate by drop dispense or spin coating methods, gases may be
trapped inside recesses in the template after the template contacts the
polymerizable material. In nano-imprint processes in which polymerizable
material is applied to a substrate by, drop dispense methods, gases may
also be trapped between drops of polymerizable material or imprint resist
dispensed on a substrate (e.g., on an imprinting stack). That is, gases
may be trapped in interstitial regions between drops as the drops spread.

[0053]Gas escape and dissolution rates may limit the rate at which the
polymerizable material is able to form a continuous layer on the
substrate or the rate at which the polymerizable material is able to fill
template features after the template contacts the polymerizable material,
thereby limiting throughput in nano-imprint processes. For example, a
substrate or a template may be substantially impermeable to a gas trapped
between the substrate and the template. In some cases, a polymeric layer
adhered to the substrate or the template may become saturated with gas,
such that gas between the imprinting stack and the template is
substantially unable to enter the saturated polymeric layer, and remains
trapped between the template and the substrate. Gas that remains trapped
between the template and the substrate may cause filling defects in the
patterned layer.

[0054]FIG. 3 illustrates gas (or gas pocket) 60 in patterned layer 46
between substrate 12 and template 18. The gas 60 may include, but is not
limited to, air, nitrogen, carbon dioxide, helium, or the like. Gas 60
between substrate 12 and template 18 may result in pattern distortion of
features formed in patterned layer 46, low fidelity of features formed in
patterned layer 46, non-uniform thickness of residual layer 48 across
patterned layer 46, or the like.

[0055]In an imprint lithography process, gas trapped between the substrate
and the template may escape through the polymerizable material, the
substrate, or the template. The amount of gas that escapes through any
medium may be influenced by the contact area between the trapped gas and
the medium. The contact area between the trapped gas and the
polymerizable material may be less than the contact area between the
trapped gas and the substrate or the template. For example, a thickness
of the polymerizable material on a substrate may be less than about 1
μm, or less than about 100 nm. In some cases, a polymerizable material
may absorb enough gas to become saturated with the gas before imprinting,
such that trapped gas is substantially unable to enter the polymerizable
material. In contrast, the contact area between the trapped gas and the
substrate or the template may be relatively large.

[0056]The gas permeability of a medium may be expressed as P=D×S, in
which P is the permeability, D is the diffusion coefficient, and S is the
solubility. In a gas transport process, a gas adsorbs onto a surface of
the medium, and a concentration gradient is established within the
medium. The concentration gradient may serve as the driving force for
diffusion of gas through the medium. Gas solubility and the diffusion
coefficient may vary based on, for example, packing density of the
medium. Adjusting a packing density of the medium may alter the diffusion
coefficient and hence the permeability of the medium.

[0057]For a multi-layer film, effective permeability may be calculated
from a resistance model, such as an analog of an electric circuit
described by F. Peng, et al. in J. Membrane Sci. 222 (2003) 225-234 and
A. Ranjit Prakash et al. in Sensors and Actuators B 113 (2006) 398-409,
which are both hereby incorporated by reference herein. The resistance of
a material to the permeation of a vapor is defined as the permeance
resistance, Rp. For a two-layer composite film with layer
thicknesses l1 and l2, and corresponding permeabilities P1
and P2, permeance resistance may be defined as:

R p = Δ p J = 1 ( P / l ) A ( 1 )
##EQU00001##

in which Δp is the pressure difference across the film, J is the
flux, and A is the area. The resistance model predicts

Rp=R1+R2 (2)

When the cross-sectional area is the same for both materials 1 and 2,
equation (2) may be rewritten as:

l 1 + l 2 P = l 1 P 1 + l 2 P 2 ( 3 )
##EQU00002##

[0058]A gas may be thought of as having an associated kinetic diameter.
The kinetic diameter provides an idea of the size of the gas atoms or
molecules for gas transport properties. D. W. Breck, Zeolite Molecular
Sieves--Structure, Chemistry, and Use, John Wiley & Sons, New York, 1974,
p. 636, which is incorporated by reference herein, lists the kinetic
diameter for helium (0.256 nm), argon (0.341 nm), oxygen (0.346 nm),
nitrogen (0.364 nm), and other common gases.

[0059]In some imprint lithography processes, a helium purge is used to
substantially replace air between the template and the substrate or
imprinting stack with helium gas. To simplify the comparison between a
helium environment and an air environment in an imprint lithography
process, the polar interaction between oxygen in air and silica may be
disregarded by Modeling air as pure argon. Both helium and argon are
inert gases, and argon has a kinetic diameter similar to that of oxygen.
Unlike oxygen, however, helium and argon do not interact chemically with
fused silica or quartz (e.g., in a template or substrate).

[0060]Internal cavities (solubility sites) and structural channels
connecting the solubility sites allow a gas to permeate through a medium.
The gas may be retained in the solubility sites. The size of the internal
cavities and the channel diameter relative to the size (or kinetic
diameter) of the gas influence the rate at which the gas permeates the
medium.

[0061]The sizes of individual interstitial solubility sites of fused
silica have been shown to follow a log-normal distribution by J. F.
Shackelford, "Gas solubility in glasses--principles and structural
implications," J. Non-Cryst. Solids 253(1999): 231-241, which is
incorporated by reference herein. As indicated by the interstitial
diameter distribution (mode=0.181 nm; mean=0.196 nm) and the kinetic
diameter of helium and argon, the number of fused silica solubility sites
available to helium exceeds the number of solubility sites available to
argon. The total number of interstitial sites is estimated to be
2.2×1028 per m3, with 2.3×1027 helium
solubility sites per m3 and 1.1×1026 argon solubility
sites per m3. The average distance between solubility sites for
helium is considered to be 0.94 nm, while the average distance between
solubility sites for argon is considered to be 2.6 nm. The structural
channels connecting these solubility sites are thought to be similar to
the helical arrangement of 6-member Si--O rings, with a diameter of about
0.3 nm. Table 1 summarizes some parameters affecting helium and argon
permeability in fused silica.

[0062]Boiko et al., "Migration Paths of Helium in α-Quartz and
Vitreous Silica from Molecular Dynamics Data," Glass Physics and
Chemistry 29(2003): 42-48, which is incorporated by reference herein,
describes behavior of helium in amorphous or vitreous silica. Within a
solubility site, the helium atom vibrates at an amplitude allowed by the
interstitial volume. The atom passes from interstice to interstice
through channels, which may be smaller in diameter than the interstices.

[0063]The parameters listed in Table 1 indicate that argon permeability in
fused silica may be very low or negligible at room temperature (i.e., the
kinetic diameter of argon exceeds the fused silica channel size). Since
the kinetic diameters of oxygen and nitrogen are larger than the kinetic
diameter of argon, air may be substantially unable to permeate fused
silica. On the other hand, helium may diffuse into and permeate fused
silica. Thus, when a helium environment is used rather than ambient air
for a nano-imprint process, helium trapped between the template and the
substrate may be able to permeate a fused silica template.

[0064]The relative porosity of similar materials may be defined as a
relative difference in density of the materials. For example, a relative
porosity of spin on glass (SOG) (density pSOG=1.4 g/cm3) with
respect to fused silica (density pfused silica=2.2 g/cm3) may
be calculated as 100%×(pfused silica)/pfused silica, or
64%. Fused silica may be used as a reference material for other materials
with oxygen-silicon bonds. For material used to form a porous layer in an
imprint lithography template, a relative density of a material with
respect to fused silica of at least about 50% or at least about 65%
provides a porosity suitable to allow movement of gases

[0065]In some cases, porogens may be added to material used to form a
portion of a template or a substrate to increase a porosity and pore size
of the material. Porogens include, for example, organic compounds that
may be vaporized, such as norbornene, α-terpinene, polyethylene
oxide, and polyethylene oxide/polypropylene oxide copolymer, and the
like, and any combination thereof. Porogens may be, for example, linear
or star-shaped. Porogens and process conditions may be selected to form a
microporous low-k porous layer, for example, with an average pore
diameter of less than about 2 nm, thereby increasing the number of
solubility sites for a range of gases. In addition, the introduction of
porogens and the increased porosity may enlarge the structure channels
connecting gas solubility sites. For pore sizes of about 0.4 nm or
greater, helium permeability of a low-k film may exceed helium
permeability of vitreous fused silica.

[0066]One method of removing gases 60 from the volume defined between
substrate 12 and template 18 includes absorption of gases 60 through
template 18. In some cases, as illustrated in FIG. 4, template 18 may be
modified to include one or more layers formed on a base layer 62. For
example, first layer 64 may be formed on base layer 62, and second layer
63 may be formed on first layer 64. When a template includes a base layer
62, a first layer 64, and a second layer 63, the first layer may be
referred to as the intermediate layer, and the second layer may be
referred to as the cap layer. When a template includes a base layer 62
and three or more additional layers, the top layer may be referred to as
the cap layer and the layers between the base layer and the cap layer may
be referred to as intermediate layers.

[0067]As noted above with respect to template 18, base layer 62 may be
formed from materials including, but not limited to, fused silica,
quartz, silicon, organic polymers, siloxane polymers, borosilicate glass,
fluorocarbon polymers, metal, hardened sapphire, and the like, or any
combination thereof. A cap layer, one or more intermediate layers, or any
combination thereof may be a porous layer. As used herein, "porous layer"
refers to a layer that is less dense and/or more porous than fused
silica.

[0068]As used herein, a thickness of a cap layer is considered to be a
thickness of the residual layer (i.e., not including the height of the
protrusions). Gas may diffuse more quickly through portions of the cap
layer from which there are no protrusions, achieving an overall increase
in helium permeability. Thus, cap layers with thinner residual layers
allow more rapid diffusion of gas through the cap layer and into the next
(e.g., porous) layer. This diffusion rate depends at least in part on the
fraction of the surface area of the template free from protrusions.
Intermediate layers and cap layers may be formed by a vapor deposition
process such as plasma enhanced chemical vapor deposition. Ranges of
process variables for forming intermediate layers and cap layers are
listed in Table 2 below.

[0069]Porosities of the cap layer and the intermediate layer may be
selected to facilitate transportation of gases 60 trapped between the
substrate 12 and the template through the cap layer and into the
intermediate layer. For example, a cap layer may be microporous,
mesoporous, or a combination thereof. That is, the pores in the cap layer
may be less than 2 nm in diameter (microporous) or between 2 nm and 50 nm
in diameter (mesoporous). An intermediate layer may be microporous,
mesoporous, or macroporous. That is, pores in an intermediate layer may
be less than 2 nm in diameter (microporous), from 2 nm to 50 nm in
diameter (mesoporous), or greater than 50 nm in diameter (macroporous).
In some cases, an intermediate layer may have regions with different
porosities. For example, an intermediate layer may have a microporous
region and a mesoporous region. Porous layers are described in U.S.
patent application Ser. No. 12/275,998, which is incorporated herein by
reference.

[0070]Sizes of the pores in a porous cap layer or porous intermediate
layer may be substantially uniform, or with a desired distribution. Pores
may range from substantially closed to fully interconnected. In some
cases, for a cap layer, a pore size or average pore size is at least
about 0.4 nm, at least about 0.5 nm, or less than about 2 nm (e.g., less
than about 1 nm, in a range between about 0.4 nm and about 1 nm, or in a
range between about 0.4 nm and about 0.8 nm). For an intermediate layer,
pore size or average pore size may be at least about 0.4 nm or at least
about 0.5 nm (e.g., up to about 1 nm, up to about 2 nm, up to about 15
nm, up to about 30 nm, up to about 40 nm, up to about 50 nm, or larger
than about 50 nm).

[0071]For template 18 with a cap layer of SiOx (thickness of about 10
nm and permeability P1), template permeability may be adjusted by
selecting porosity and pore size of one or more intermediate layers. The
effect of the permeability and thickness of the intermediate layers(s) on
the effective permeability of a multi-layer composite imprinting stack
with a thickness of 310 nm is shown in Table 3.

[0072]Table 3 suggests that increasing a thickness of the intermediate
layer alone may yield a higher effective permeability than increasing the
permeability of the intermediate layer alone. That is, for composite
imprinting stacks with a total thickness of 310 nm and having an
intermediate layer thickness of 100 nm, 200 nm, or 300 nm and a cap layer
thickness of 10 nm, the effective permeability increases twenty-fold,
from 1.5 P1 to 2.8 P1 to 30.1 P1, respectively, over the
200 nm increase in intermediate layer thickness. For an intermediate
layer thickness of 300 nm and a cap layer thickness of 10 nm, a ten-fold
increase in permeability of the intermediate layer from 100 P1 to
1000 P1 increases the effective permeability from 23.8 P1 to
30.1 P1.

[0073]In some cases, as shown in FIG. 5, an imprint lithography template
may include a base layer and a first layer. The first layer may be a
porous layer. The first layer may be patterned, and may be thought of as
a cap layer. Referring to FIG. 5, a porous layer 61 can be formed on a
base layer 62. Porosity of the porous layer 61 may be non-uniform or
asymmetric, as shown in FIG. 5, or substantially uniform. Porous layer 61
may be a cap layer. In some cases, porous layer 61 may have a porosity
gradient, shown by the distribution of pores 65, such that the density of
the layer is higher near the top surface of the layer (i.e., the surface
in contact with the imprint resist during use). The porosity gradient may
include changes in average pore size, pore size distribution, and/or pore
density. The gradient may improve the mechanical strength of the features
that are etched directly into the porous layer, while allowing diffusion
of gases into the porous layer. That is, reduced porosity near the top of
the cap layer (e.g., reduced porosity of the protrusions and proximate
the protrusions) may yield a patterned portion with more mechanical
strength than a cap layer with a higher porosity near the top of the cap
layer. In some cases, the porous layer 61 may have a substantially
uniform density in the portion of the layer that is etched to form the
protrusions and recessions. The porous layer 61 may have microporous,
mesoporous, or macroporous regions, or any combination thereof.

[0074]As shown in FIG. 6, a template 18 may be formed as a unitary
structure with a porosity and average pore size selected to allow
efficient diffusion of a gas while maintaining mechanical strength near
the top of the cap layer. Templates made from, for example, organic
polymers, inorganic materials (e.g., silicon carbide, doped silica,
VYCOR®), and the like, or any combination thereof, may have a lower
packing density, and therefore a higher gas (e.g., helium) permeability,
than vitreous fused silica. Template 18 consists essentially of a single
porous layer. The porous layer is not adhered to a base layer. Template
18 may be smooth or patterned. Template 18 may be an asymmetric porous
layer, as shown in FIG. 6, or a symmetric porous layer.

[0075]As shown in FIG. 7, a template 18 may include a first layer 64 and a
second layer 63. First layer 64 may be a porous layer. Second layer 63
may be a cap layer. As with template 18 in FIG. 6, the first layer is not
adhered to a base layer. The second layer 63 may inhibit penetration of
the polymerizable material into the porous material. The second layer 63
may also impart desirable surface properties, mechanical properties, and
the like to the template. Template 18 may be smooth or patterned. First
layer 64 may be an asymmetric porous layer.

[0076]Microporous layers may be advantageous in imprint lithography
applications. For example, microporous layers may have pores large enough
to allow diffusion of trapped gas through the pores, but small enough to
inhibit penetration of the pores by polymerizable fluid or other
substances. Microporous cap layers may have sufficient mechanical
strength to withstand repeated use without cracking, buckling, or
delaminating. Compared to patterned mesoporous and macroporous layers,
patterned microporous layers may have smoother sidewalls and smaller void
defects inside etched features.

[0077]In some cases, pores at a surface of a template (e.g., in a cap
layer or other porous layer), if not sealed, may allow penetration of
polymerizable fluid or other substances into the template, which may
cause clogging of the pores or added stress during an imprinting process.
If pores near a surface of a template are sufficiently small, sealing of
the pores may not be needed to inhibit penetration of polymerizable fluid
or other substances into the pores. In some cases, however, it is
advantageous to seal or fill exposed pores (e.g., with a less porous
silicon oxide layer) by using a thin film deposition method that produces
substantially continuous, conformal, ultrathin gas-permeable films to
inhibit disadvantageous penetration, clogging, saturation, and the like,
of the template by polymerizable fluid or other substances. Pore sealing
may be accomplished by a number of methods including, but not limited to,
vapor-based film deposition processes such as chemical vapor deposition
(CVD), atomic layer deposition (ALD), plasma-assisted atomic layer
deposition (PA-ALD), pulsed plasma-enhanced chemical vapor deposition
(pulsed-PECVD), molecular layer deposition (MLD), and physical vapor
deposition (PVD), or by solution-based film deposition methods such as
dip coating and spin coating, or plasma treatment. PA-ALD is described in
US patent Application Publication No. US 2007/0190777, which is
incorporated herein by reference. Pulsed-PECVD is described in U.S.
Patent Application Publication No. 2008/0199632, which is incorporated
herein by reference.

[0078]The selection of a seal layer deposition process and film
composition can depend on several factors, including the size and/or
geometry of template protrusions and recesses, the exposed pore diameter
in the porous film, the desired permeability and mechanical properties of
the seal layer, and the ability of the seal layer to interact with
release agents, etc.

[0079]FIG. 8A shows a porous template 18 with a base layer 62, first
intermediate layer 64, cap layer 63, and seal layer 59. Seal layer 59 may
be made from materials including, but not limited to: metal oxides,
nitrides, carbides, oxynitrides, oxycarbides, or polymers such as
organo-silanes and polyxylylenes. A thickness of seal layer 59 on the
surface of a porous layer may be less than about 10 nm, less than about 5
nm, less than about 3 nm, or, in some cases, about two times greater than
the pore radius. In some cases, the pore sealing deposition method may be
selected to substantially confine the reaction and growth of seal layer
59 to the surface of the porous layer. In certain cases, the seal layer
reactants may be allowed to penetrate several nanometers into the porous
layer.

[0080]Pore sizes in seal layer 59 may be larger than the kinetic diameter
of the gas in the imprint environment to facilitate the diffusion of the
gas into the adjoining porous layer. Pore sizes in seal layer 59 may be
less than about 2 nm, less than about 0.8 nm, or less than about 0.6 nm,
such that helium is able to diffuse through the seal layer. Seal layer 59
may be selected such that atoms or molecules larger than helium, oxygen,
nitrogen, or carbon dioxide may be unable to diffuse through the seal
layer. The material used to form seal layer 59 may be selected to
withstand repeated use in nano-imprint lithography processes, including
piranha, dilute base, ozone, or plasma cleaning processes. In some cases,
seal layer 59 may be selected to be a non-permanent or sacrificial layer
which is intended to be removed and replaced.

[0081]FIG. 8B illustrates a porous template 18 with a base layer 62,
porous intermediate layer 64, seal layer 59, and cap layer 63. The seal
layer preferably has pores large enough for helium to pass through, but
small enough to substantially block reactive species in vapor or liquid
phase from penetrating the porous layer during cap layer deposition. Seal
layer 59 may have a thickness of about 1 nm to about 10 nm, or less than
about 5 times the pore radius, less than about 3 times the pore radius,
or about two times the pore radius. Seal layer 59 may include, for
example, silicon oxide (SiOx). In some cases, rather than seal the
surface pores completely with a continuous film, a seal layer process may
be used to decrease the open pore size of the porous layer.such that
diameters of the pores inhibit the penetration (e.g., diffusion) of cap
layer components into the porous layer.

[0082]The presence of the seal layer beneath the cap layer (e.g., between
the cap layer and the porous layer) allows a clear transition from the
cap layer to the porous layer, and inhibits penetration of pore-clogging
contaminants into the porous layer. For example, seal layer 59 may
inhibit penetration of reactive species present during formation of the
cap layer 63 into porous layer 64. Penetration and pore clogging of the
porous layer increases the density of the porous layer near the interface
between the porous layer and, for example, the cap layer, and thus makes
it difficult to ascertain the location of the interface during etching.
The presence of a seal layer below the cap layer would maintain the
integrity of the interface, and reduce or substantially eliminate
ambiguity as to the required etch depth of the features in the cap layer.
Thus, the deposition of a seal layer on the porous layer enables the etch
process, because it is advantageous to have as little cap layer material
between the bottom of the feature and the porous layer underneath. This
distance is indicated by d in FIG. 8B.

[0083]In an example, a, porous layer is deposited on a base layer. A thin
(e.g., 5 nm), dense pore seal layer is formed on the porous layer, and a
dense cap layer (95 nm) is formed on the seal layer. The total thickness
of the dense coating is 100 nm. If the cap layer is etched to a depth of
90 nm, then d=10 nm, and 10 nm of dense film separates the bottom of the
feature from the underlying porous film. In the absence of a seal layer,
then several nanometers of the porous layer may have become blocked and
the film density profile may vary with depth, all of which make it more
difficult to determine how far to etch features in to the cap layer so
that the features reside in a uniformly dense film with a known distance
to the porous layer underneath. Some methods of pore sealing include ALD,
PA-ALD, and pulsed PECVD, as well as other methods mentioned herein. Use
of a method such as ALD to form the cap layer as well as the seat layer
would limit throughput and increase production costs.

[0084]As described herein, a pore seal layer may allow optical thickness
measurements of the cap layer if the refractive index of the seal layer
differs from the refractive index of the cap layer. For example, a cap
layer may be deposited on top of the seal layer and then polished back to
a known measurable distance from the seal layer.

[0085]In some cases, a less porous seal layer and a cap layer may be
deposited on a more porous layer (e.g., intermediate layer) at
temperatures less than, equal to, or greater than that used for
deposition of the more porous layer. Although the less porous layer may
be deposited at a higher temperature than that used for the more porous
layer beneath it, it may be desirable in some cases to deposit the less
porous layer at a temperature equal to or less than the deposition
temperature of the more porous layer if thermal effects during the less
porous layer deposition induce undesirable changes to pore size, pore
size distribution, pore interconnectivity, and the like in the more
porous layer.

[0086]The material used to form a porous cap layer or a porous
intermediate layer may be selected to withstand repeated use in
nano-imprint lithography processes, including piranha, dilute base, and
ozone, or plasma cleaning processes. In some cases, a porous cap layer or
a porous intermediate layer may be designed for limited use, and may not
need the ability to withstand a cleaning process. Adhesion of an
intermediate layer to a base layer and to a cap layer may be, for
example, at least about three times the force required to separate the
template from the patterned layer formed in an imprint lithography
process. Material properties to be considered in selection of porous
materials include adhesion to the base layer, coefficient of thermal
expansion, thermal conductivity, refractive index, and UV light
transmittance and absorbance. For example, a material with low UV
absorbance allows UV radiation to pass through a cap layer or an
intermediate layer of a template to polymerize the imprint resist without
generating a disadvantageous amount of heat proximate the imprint resist.
In certain embodiments, Young's modulus of the porous material may be,
for example, at least about 2 GPa, at least about 5 GPa, at least about
10 GPa, or at least about 20 GPa.

[0087]In some applications, a template will be required to make hundreds
or even thousands of imprints before it has satisfied its cost of
ownership objective, therefore materials used for the porous layer must
have sufficient mechanical strength to survive this number of imprints
without cracking, buckling, or delaminating. A porous material with a
selected Young's modulus, in combination with a selected relative density
and refractive index may be used to form a porous layer with unexpected
advantages, including a decrease in filling time, allowing
high-throughput in a fabrication process, and a simultaneous ability to
withstand mechanical forces present during the imprinting process. This
combination of desirable properties allows increased process longevity
and low template defectivity.

[0088]The ratio of the Young's modulus of a porous material including
silicon and oxygen to the relative density of that material with respect
to fused silica, is an indicator of the ability of a porous material to
perform as a porous layer in an imprint lithography template. A porous
silicon- and oxygen-containing material that provides desirable
throughput and durability may have a ratio of Young's modulus to relative
density of the material with respect to fused silica of at least about
10:1, at least about 20:1, or at least about 30:1.

[0089]Optical-based processes related to imprint lithography templates
include, for example, optical-based template pattern inspection. To
facilitate optical-based processes, the refractive index of a porous
layer may be similar to the refractive index of other layers in the
template (e.g., cap layer, seal layer) on the same template, such that
unwanted optical effects (e.g., bending of light and related distortion)
are reduced during processes including measurement processes and
inspection processes. The refractive index for fused silica is 1.46. When
fused silica is used as a base, it may be desirable for other layers of
an imprint lithography template to have a refractive index close to that
of fused silica. For increased optical compatibility with other layers in
an imprint lithography template, the refractive index of a porous layer
in an imprint lithography template may be between about 1.4 and about 1.5

[0090]A porous layer (e.g., a porous intermediate layer) may be made from
materials including, but not limited to, silicon oxide, anodic aluminum
oxide (AAO), organo-silanes, organo-silicas, organosilicates, organic
polymers, inorganic polymers, and the like, or any combination thereof.
In some embodiments, a porous layer may include low-k, porous low-k, or
ultra-low-k dielectric film. Low-k dielectric films used in the
semiconductor industry, i.e. organosilicate glass (OSG) films deposited
by CVD of organosilanes or by spin-coating of silsesquioxanes, may
contain sufficient porosity to enhance gas diffusion and decrease filling
time, however their mechanical properties (elastic modulus, E<10 GPa;
hardness, H<2 GPa) are poorer than fused silica. Porous layers
including organic or inorganic polymers are also have much lower
mechanical properties compared to fused silica. Anodic aluminum oxide
(AAO) films have higher Young's modulus (˜140 GPa) than fused
silica with high porosity, but also have a higher refractive index
compared to fused silica (˜1.7 vs. 1.46), thus in this regard AAO
may be less desirable as a porous layer when capped with a silicon oxide
film when optical pattern inspection is considered.

[0091]A base layer and an intermediate layer or a cap layer may be formed
of the same or different materials. In some cases, a cap layer may be
more porous than base layer (e.g., to allow gases to diffuse through the
cap layer and into an intermediate layer). In some cases, a cap layer may
be less porous than intermediate layer (e.g., to facilitate successful
etching of the cap layer to form a desirable patterned surface). In some
embodiments, the cap layer is more porous than the base layer and less
porous than the intermediate layer. A cap layer may be formed by material
selected to achieve desirable wetting and release performance during an
imprint lithography process.

[0092]In some embodiments, a cap layer may include a film of porous
SiOx with 1≦×≦2.5. For example, as used herein,
"porous SiOx" refers to silicon oxide that is more porous than fused
silica, less dense than fused silica, or both. A thickness and
composition of the cap layer may be chosen to provide mechanical strength
and selected surface properties, as well as permeability to gases that
may be trapped between a substrate and a template in an imprint
lithography process.

[0093]A thickness of an intermediate layer may be, for example, in a range
of about 10 nm to about 100 μm, or in a range of about 100 nm to about
10 μm. A thickness of an intermediate layer may be increased to
increase the capacity of the layer to accommodate diffusion of gases into
the layer. In some cases, a thicker intermediate layer may provide higher
effective permeability without significantly reducing UV transparency,
thermal expansion, and the like.

[0094]A thickness of a cap layer may be in a range of about 10 nm to about
10,000 nm (e.g., in a range of about 10 nm to about 50 nm, about 50 nm to
about 100 nm, about 100 nm to about 500 nm, about 500 nm to about 1000
nm, or about 1000 nm to about 10,000 nm). Diffusion of gas through a cap
layer is related to the porosity of the cap layer as well as the
thickness of the cap layer. In some cases, a thickness of a cap layer may
be selected based at least in part on the porosity of the cap layer. That
is, a more porous cap layer may be thicker (e.g., about 5000 nm) than a
less porous cap layer (e.g., about 10 nm), such that gas can diffuse
relatively quickly through porous cap layers of various porosities and
thicknesses. If a cap layer is more porous than the layer to which it is
adhered, a thickness of a cap layer may be increased to increase the
capacity of the layer to accommodate diffusion of gases into the layer.
If the cap layer is adhered to a more porous film, then it may be
desirable to decrease the thickness of the cap layer between the bottom
of an etched feature and the more porous layer to decrease diffusion
resistance.

[0095]An intermediate layer may be formed by vapor deposition,
solution-based methods, thermal growth methods, or the like on a base
layer or on another intermediate layer. A cap layer may be formed by
vapor deposition, solution-based methods, thermal growth methods, or the
like on an intermediate layer or a base layer. As used herein, "vapor
deposition" generally refers to a process in which a layer is formed from
a vaporized precursor composition on a surface of a substrate. Vapor
deposition processes include, but are not limited to, chemical vapor
deposition (CVD), atomic layer deposition (ALD), and physical vapor
deposition (PVD). CVD processes include, for example, plasma-enhanced CVD
(PECVD), low-pressure CVD (LPCVD), sub-atmospheric CVD (SACVD),
atmospheric pressure CVD (APCVD), high density plasma CVD (HDPCVD),
remote plasma CVD (RPCVD), and the like. PVD processes include
ion-assisted e-beam methods, and the like.

[0096]By varying the process conditions and materials, porous layers with
different mean pore sizes and pore size distributions (e.g., different
porosity or relative porosity) may be produced. An intermediate layer
and/or a cap layer may have pores with a larger pore size and a greater
porosity than fused silica. As used herein, "porosity" refers to the
fraction, as a percent of total volume, occupied by channels and open
spaces in a solid. The porosity of an intermediate layer may range from
about 0.1% to about 60% (e.g., about 1% to about 20%, or about 5% to
about 15%). In some cases, the porosity of an intermediate layer may be
at least about 10%, or at least about 20%. The porosity of a cap layer
may range from about 0.1% to about 20% (e.g., from about 1% to about 20%,
or from about 3% to about 15%).

[0097]Depositing SiOx by a vapor deposition process (e.g., PECVD) can
yield a film with higher porosity than other processes such as thermal
oxidation or flame hydrolysis deposition. Vapor deposition conditions
that can be varied include temperature, pressure, gas flow rates (e.g.,
for the silicon-containing gas, the oxidation gas, the carrier gas, etc.,
or ratios thereof), electrode distance, RF power, and bias.

[0098]In an example, oxide deposition from silane-PECVD can occur
according to the reaction shown below:

SiH4(g)+2N2O.sub.(g)→SiO2(s)+2N2(g)+2H2(g)-
.

Organosilicon materials such as tetraethyl orthosilicate (TEOS),
tetramethylsilane (TMS), and hexamethyldisilazane (HMDS) may also be used
with PECVD to form SiOx films.

[0099]The density of PECVD SiO2 has been shown by Levy et al. ("A
comparative study of plasma enhanced chemically vapor deposited Si--O--H
and Si--N--C--H films using the environmentally benign precursor diethyl
silane," Mater. Lett. 54 (2002): 102-107, which is incorporated herein by
reference), to vary from 1.5 g/cm3 to 2.2 g/cm3 at deposition
temperatures between 100° C. and 350° C. The Young's
modulus increased from 25 GPa to over 70 GPa over this temperature range.
PECVD has been reported to generate silicon oxide films with a Young's
modulus as high as 144 GPa at deposition temperatures of 250° C.
to 350° C. (Bhushan et al., "Friction and wear studies of silicon
in sliding contact with thin-film magnetic rigid disks," J. Mater. Res. 9
(1993) 1611-1628; and Li et al., "Mechanical characterization of
micro/nanoscale structures for MEMS/NEMS applications using
nanoindentation techniques," Ultramicroscopy 97 (2003) 481-494, both of
which are incorporated by reference herein).

[0100]A Young's modulus of 25 GPa is substantially higher than the Young's
modulus of films obtained from porous semi-conductor low-k films,
including organosilicate glass films deposited by CVD of organosilanes or
by spin-coating of silsesquioxanes. The hardness of a PECVD SiOx
film deposited at temperatures greater than about 150° C. may also
exceed the hardness of a semi-conductor low-k film. A PECVD SiOx
film deposited at about 350° C. may have about 5% microporosity,
as described by Devine et al. ("On the structure of low-temperature PECVD
silicon dioxide films," J. Electron. Mater. 19(1990) 1299-1301, which is
incorporated by reference herein).

[0101]SiOx deposited on a fused silica substrate by PECVD displays
compressive stress believed to originate at least in part from a mismatch
of coefficients of thermal expansion. This mismatch may be reduced by
thermal annealing at moderate temperatures (e.g., a 500° C.
thermal cycle), as described by Cao et al. ("Density change and viscous
flow during structural relaxation of plasma-enhanced
chemical-vapor-deposited silicon oxide films," J. Appl. Phys. 96(2004)
4273-4280, which is incorporated herein by reference). With selected
annealing conditions, the nature of the stress may become more tensile in
nature, while still maintaining a compressive to neutral stress desirable
for a porous layer in an imprint lithography template. As shown by Cao et
al., the coefficient of thermal expansion of a 10 μm thick PECVD
SiOx film after a 500° C. thermal cycle (about 0.55
ppm/° C.) is similar to that of fused silica.

[0102]In some cases, annealing of a PECVD SiOx template layer may
promote densification of the SiOx film, resulting in lower
permeability. However, an annealing process carried out at lower
temperatures (e.g., about 100° C. to about 350° C.) under
controlled conditions (e.g., heating and cooling rates) may maintain the
porosity of the film.

[0103]Low temperature annealing experiments were carried out to evaluate
the impact of annealing on film stress. As shown in Table 4, a PECVD
SIOx film (thickness of 5 μm) on fused silica had a calculated
stress of -94 MPa after deposition. Following a first 140° C.
annealing cycle, the stress was calculated as -57 MPa. Following a second
140° C. annealing cycle, the stress was calculated as -42 MPa. The
stress was calculated by the Stoney equation. Radii were determined by
measurements with a laser interferometer (Mark GPI xps, available from
Zygo Corporation, Middlefield, Conn.), and film thickness was measured
with a spectroscopic reflectometer (available from Metrosol, Austin,
Tex.).

[0104]In some cases, forming a cap layer (e.g., a SiOx cap layer)
with a vapor deposition process on an intermediate layer may clog pores
in the intermediate layer. To reduce clogging of pores in the
intermediate layer, the intermediate layer may be pre-saturated with
inert gas. An exemplary PECVD process to reduce clogging of pores in a
porous substrate is shown in the flow chart in FIG. 9. In process 90,
after pumping the chamber (step 91), purging the chamber (step 92), and
pumping the chamber again (step 93), one or more inert gases are used to
pre-saturate the chamber and the porous substrate (step 94). The flow of
inert gases is stopped, and the CVD gases are introduced to the chamber
and the plasma is started (step 95).

[0105]In process 90, the CVD layer is thought to grow from the surface of
the intermediate layer for several reasons. For example, since the pores
have been saturated by inert gases, it is difficult for CVD gases to
diffuse into the intermediate layer. Additionally, even though some of
the CVD gases may get into the porous intermediate layer, they are
diluted with the inert gases inside the intermediate layer and may not be
present in sufficient quantity to form a dense structure capable of
blocking the pores after reaction. Furthermore, since the plasma starts
at substantially the same time as the CVD gases are introduced into the
chamber, the reaction starts right away, and the CVD gases have limited
time to diffuse into the intermediate layer.

[0106]FIG. 10 illustrates a process of capping a porous first layer 64
(e.g., an intermediate layer) with a thin layer of vapor deposited SiO,
as a second layer 63 (e.g., a cap layer) according to the steps in FIG.
9. This process could also be applied in the sealing of a cap, or the
sealing of an asymmetric porous layer. As shown in FIG. 10, porous first
layer 64 is saturated with inert gas 65. Gas 69 (including
silicon-containing gas, oxidation gas, carrier gas, etc.) is introduced
in a CVD process to form silica second layer 63 on porous first layer 64.
After second layer 63 is formed on the surface of porous first layer 64,
the porous first layer will be effectively sealed, such that diffusion of
the vapor deposited gases, polymerizable material, and the like, into the
porous first layer is reduced or eliminated.

[0107]The gases used for pre-saturation may be inert toward selected vapor
deposition processes or may not react inside the porous layer to clog the
pores. The inert gas may be helium, neon, argon, or nitrogen, or the
like. In some cases, the vapor deposition gas may be used as the inert
gas. For example, in a PECVD SiOx deposition process with SiH4
and N2O, N2O may be used to pre-saturate a porous layer.
Smaller molecule gases such as helium and neon may diffuse out after the
process if their kinetic diameters are smaller than the pore size of the
seal layer. Larger molecule gases such as argon and nitrogen might be
trapped inside the a porous layer if their kinetic diameters are larger
than the pore size of the seal layer. Gases trapped inside the porous
layer may cause complications in future applications. Therefore, smaller
molecule gases may be preferred.

[0108]Pre-saturation 91 in process 90 may range from about 5 seconds to
about 60 min. The inert gas pressure may be at least the same as the
total vapor deposition gas pressure used for the vapor deposition process
and in some cases higher than the total vapor deposition gas pressure. An
initial deposition rate might be slightly slower due to the dilution
effect by the inert gases. To achieve more precise vapor deposition layer
thickness control, the deposition rate may be re-calibrated between
procedures. Different inert gases may result in different initial
deposition rates. The deposition rate may to be re-calibrated when
changing to a different inert gas. Different inert gas pressure may also
result in a different initial deposition rate. The deposition rate may be
re-calibrated when changing to a different pre-saturation pressure.

[0109]In certain circumstances, a porous layer may be subject to internal
tensile stress that leads to cracking or delaminating of the film. As
illustrated in FIG. 11, porous layer 68 may be subject to intrinsic
forces that produce a tensile force FT (or compressive force
FC) affecting the porous layer. For example, tensile force FT
(or compressive force FC) may result in separation of porous layer
68 from base layer 62, angular deformation, and the like.

[0110]The stress in a porous layer or film at ambient conditions (e.g.,
room temperature, atmospheric pressure) may be tensile to compressive
(e.g., about +1 GPa to about -3 GPa, respectively). The stress of a vapor
deposited porous layer may be managed by a number of methods, such as
control of deposition conditions, annealing, or stress relief films or
layers.

[0111]Template 18 may include one or more relief layers 66 designed to
mitigate the effects (e.g., template curvature) of tensile force FT
acting on porous layer 68. For example, relief layer 66 may be designed
having materials formed in a compressive state such that compressive
force FC acts on relief layer 66. For example, relief layer 66 may
be designed from materials providing a set intrinsic stress level
resulting in compressive force FC. As such, compressive force
FC acting on relief layer 66 substantially neutralizes the tensile
force FT acting on porous layer 68 within template 18. In some
embodiments, one or more relief layers 66 may be designed to mitigate the
effects of compressive force FC (not shown) acting on porous layer
68.

[0112]For example, FIG. 12 illustrates an exemplary embodiment of template
18 having porous layer 68 adjacent to relief layer 66. Relief layer 66
may be formed of materials providing a compressive force FC such
that compressive force FC substantially reduces the effects of
tensile force FT acting on porous layer 68. Relief layer 66 may be
positioned on, substrate layer 62 using techniques such as spin-coating,
dip coating, CVD, PVD, thin film deposition, thick film deposition, or
the like, or any combination thereof. The relief layer 66 may be formed
of material including, but not limited to SiNx, SiOxNy, SiCx, SiOx,
DLC, and the like, or any combination thereof. In some cases, relief
layer 66 may be substantially transparent to UV light or wavelengths of
light used during the imprint process. Relief layers 66 may be permeable
to gases such as helium, nitrogen, oxygen, carbon dioxide, and the like.
In some embodiments, one or more relief layers 66 may be designed to
provide a tensile force FT such that tensile force FT
substantially reduces the effects of compressive force FC (not
shown) acting on porous layer 68.

[0113]FIG. 13A illustrates an exemplary embodiment of template 18 having
multiple relief layers 66a and 66b adjacent porous layer 68. Porous layer
68 may be permeable to gases such as helium, nitrogen, oxygen, carbon
dioxide, and the like. Relief layers 66a and 66b may be formed of
materials providing compressive forces FC1 and FC2. Compressive
forces FC1 and FC2 may be similar or different in magnitude,
depending on design considerations. For example, compressive force
FC2 of relief layer 66b may reduce the effects of tensile force
FT on porous layer 68 (e.g., may reduce bending of the layer).

[0114]Relief layers 66a and 66b may be positioned on substrate layer 62
and porous layer 68, respectively, using techniques such as spin-coating,
dip coating, chemical vapor deposition (CVD), physical vapor deposition
(PVD), thin film deposition, thick film deposition, or the like, or any
combination thereof. Relief layers 66a and 66b may use similar
positioning methods or different positioning methods depending on design
considerations.

[0115]Additionally, relief layers 66a and 66b may be formed of similar
materials or different materials depending on design considerations. For
example, as relief layer 66a may be positioned within the diffusion path
of gases 60 (not shown), relief layer 66a, having a thickness tR1,
may be formed of materials permeable to gases 60 present during the
imprint process. Alternatively, relief layer 66b may have a thickness
tR2 that is greater than thickness tR1 and may be formed of
less permeable materials as the majority of stress compensation may occur
at relief layer 66b. Additionally, relief layer 66b may be formed of
permeable material to facilitate diffusion of gases into substrate layer
62, depending on design considerations. In some embodiments, as
illustrated in FIG. 13B, relief layer 66a may be a patterned relief layer
66a having features 24 and 26 formed therein. In some embodiments, relief
layers 66a and 66b may be formed of materials providing tensile forces
FT1 and FT2 to reduce the effects of compressive force FC
(not shown) on porous layer 68.

[0116]FIG. 14 illustrates an exemplary embodiment of template 18 having
multiple relief layers 66 to relieve tensile stress within multiple
porous layers 68. In particular, template 18 comprises relief layers
66c-e that may be interspersed between permeable layers 68a and 68b such
that compressive forces FC1-C3 reduce the effect of (e.g., the
bending moments caused by) tensile forces FT1-T2. Relief layers
66c-e may use similar positioning methods or different positioning
methods depending on design considerations. Additionally, relief layers
66c-e may be formed of similar materials and have similar physical
characteristics (e.g., thickness) and/or different materials and physical
characteristics depending on design considerations. An analogous
embodiment may provide relieve of compressive stress FC1-C3 caused
by tensile forces FT1-T2 (not shown).

[0117]Referring to FIG. 15A, template 110 shows stress indicated as
bending of layer or film 112 on the imprinting surface of the template.
Referring to FIG. 15B, stress relief layer 114 is formed on the surface
of template 110 opposite layer 112. Stress relief layer 114 relieves the
stress in layer 112 by providing a bending moment which reduces the
curvature of the layer. In some embodiments, stress relief layer 114 may
provide compressive stress to reduce compressive stress of layer 112. In
some embodiments, stress relief layer 114 may provide tensile stress to
reduce tensile stress or to impart a compressive stress to layer 112.

Etch Stop layer

[0118]Referring to FIG. 16, template 100 includes a base layer 102, an
etch stop layer 104, and a top layer 106. Etch stop layer 104 and top
layer 106 differ with respect to certain physical properties (e.g., index
of refraction), such that interface 108 between the etch stop layer and
the top layer can be used as a reference point during nano-imprint
lithography fabrication processes that include etching or chemical
mechanical planarization (CMP) of the top layer. Etch stop layer 104 and
top layer 106 also differ with respect to certain chemical properties
(e.g., reactivity with known etching processes).

[0119]Template 100 may be, for example, bulk fused silica. Etch stop layer
104 may be substantially UV transparent and have low UV absorbance. In an
example, etch stop layer 104 may include a metal, a metal oxide, or a
metal nitride. In some cases, etch stop layer 104 consists essentially of
SixNy. Top layer 106 may be porous (e.g., porous silica). In
some cases, top layer 106 includes SiOx, with
1≦×≦2.5.

[0120]The different physical characteristics of the etch stop layer 104
and the top layer 106 (e.g., different indices of refraction) allow
optical/metrological assessment of the thickness of the top layer, as
measured with respect to the interface 108 between etch stop layer 104
and top layer 106. Because a depth of top layer 106 can be accurately and
precisely measured with respect to etch stop layer 104, top layer 106 can
be polished back (e.g. with chemical mechanical planarization) to a known
measurable distance from the etch stop layer 104 to enable etching
processes in nano-imprint lithography template fabrication used to
pattern top layers with known and reproducible dimensions (e.g., residual
layer thickness, protrusion height, aspect ratio, and the like).

[0121]Etching processes that etch top layer 106 but not etch stop layer
104 may include any etching process that is known to etch silica (e.g.,
reactive ion etching). Thus, the different chemical properties of the
etch stop layer 104 and the top layer 106 allow etching of the top layer
without etching of the etch stop layer. The presence of etch stop layer
104 allows the top layer 106 to be completely removed by etching while
leaving the etch stop layer and the base layer substantially unaltered.
Thus, top layer 106 can be removed, changed, or replaced, as desired. The
ability to reuse the base layer of the template is economically
advantageous, and allows conservation of resources.

Metrology Marker

[0122]In some cases, a region of a base layer or intermediate layer of an
imprint lithography tem 100 plate may be coated with a marker film. FIG.
17A illustrates an imprint lithography template 100 with base layer 102,
top layer 106, and marker region 107 formed at an interface between the
base layer and the top layer. Marker region 107 may cover a small portion
of the base layer 102 (e.g., less than about 1 cm2). A thickness of
marker region 107 may be between about 2 nm and about 30 nm, such that a
flatness of the upper surface of the top layer is substantially
unaffected by the presence of the marker region. In some cases, top layer
106 may be polished smooth and flat (e.g., with chemical mechanical
planarization) before patterning and etching features on the template. A
thickness of marker region 107 may be used as a reference to determine a
depth of etching of top layer 106. The material used to form marker
regions 107 may include, for example, a metal, a metal oxide, or a metal
nitride.

[0123]One or more marker regions 107 may be spaced apart from an active
(e.g., patterned) portion of the top layer 106. Placing a metrology
marker outside the mesa (e.g., placing four markers outside the corners
of the mesa) would allow UV radiation to pass through the template and
into the polymerizable fluid without blocking, and would reduce the total
amount of radiation absorbed (and thus the amount of heating of the
template) compared to a continuous stop etch layer.

[0124]In some cases, rather than depositing a small marker region, one or
more areas of a template may be masked during coating of a base layer or
coating of an intermediate layer with another layer (e.g., a porous
layer). A difference in height between the masked area 109 and the coated
portion 111 may serve as a reference for coating depth, etching depth, or
polishing depth.

[0125]FIG. 17B illustrates a nano-imprint lithography template with marker
regions 107 deposited on base layer 102. Porous layer 103 is formed over
base layer 102 and marker regions 107. Porous layer 103 may be polished
before seal layer 105 is deposited on the porous layer. The seal layer
may inhibit dogging of the porous layer during formation of cap layer
106. That is, during formation of cap layer 106, the presence of the seal
layer may inhibit infiltration and thus clogging of the porous layer with
components (e.g., reactive species) used to form the cap layer. In some
cases, based on the properties of porous layer 103 and the cap layer 106,
the seal layer 105 may be omitted.

Chemical Mechanical Planarization

[0126]In embodiments discussed herein, a layer of a template (e.g., a cap
layer, an intermediate layer) may undergo chemical mechanical
planarization (CMP). CMP includes the polishing of one or both sides of a
substrate simultaneously, using both chemical and mechanical means. An
imprint lithography template is held in a carrier housing. Slurry is
dispensed on a polishing pad. The template is rotated and oscillated
(eccentric motion) and is brought into contact with a rotating polishing
pad. The force of the substrate against the pad is controlled. The slurry
both reacts with the surface (chemical aspect of CMP) and physically
scrubs the surface (mechanical aspect of CMP). The abraded material is
carried away by the polishing pad.

[0127]Surfaces formed by some PECVD processes, such as silicon oxide film
deposition, may be undesirably rough. The roughness reduces the
usefulness and desirability of these surfaces for use as an imprint
surface for patterning, or for use as a base layer for the deposition of
a conformal film. CMP can be used to polish a rough layer to
substantially eliminate the roughness and improve flatness and
parallelism of the template. CMP may also improve filling speed by
reducing a roughness of a layer that contacts the imprint resist.

EXAMPLES

Example 1

[0128]The enhanced diffusion performance of low-temperature PECVD
SiOx was shown through imprint testing. Samples for imprint filling
tests were generated by depositing porous silicon oxide by PECVD
(PlasmaTherm 790 RIE/PECVD) at 200° C. to a thickness of 5 μm
on double-side polished (DSP) 3'' silicon wafers having a nominal
thickness of 375 μm. The Si source was SiH4, with a flow rate of
21.2 sccm. The oxidizing agent was N2O, with a flow rate of 42 sccm.
The deposition total pressure was 300 mTorr, and the RF power was 50 W.
The wafer was placed directly on the chuck for deposition. The wafers
were then spin-coated with 60 nm of TranSpin® (available from
Molecular Imprints, Inc., Austin, Tex.). As a control, a 3'' DSP silicon
wafer was coated with 60 nm of TranSpin®. A 65 mm fused silica
core-out template was used to generate imprints with a residual layer
thickness of about 90 nm using a grid drop pattern with a 340 μm drop
center-to-center distance. Helium was used as the purge gas.

Example 2

[0129]FIGS. 18A and 18B show images of drops of imprint resist 180 in a
helium environment taken through a template including a 5 μm porous
silicon oxide cap layer formed on the wafer by PECVD. As shown in FIG.
18A, drop interstitial regions 182 were observed by a microscope camera
at the time the template contacted the resist. The image in FIG. 18B was
taken 1 second after the template contacted the resist. Within 1 second
after the resist was contacted by the template, gas pockets in the
interstitial locations 182 disappeared, and imprint resist 180 spread to
substantially cover the template.

[0130]FIGS. 19A-19C show images of drops of imprint resist 180 in a helium
environment taken through a template similar to that in FIG. 18A, without
the 5 μm porous silicon oxide cap layer. FIG. 19A shows drops of
imprint resist 180 and interstitial regions 182 as observed by a
microscope camera at the time the template contacted the resist. FIGS.
19B and 19C show interstitial regions 182 still present 1 second later
and 4 seconds later, respectively. Thus, the porous oxide layer allowed
for the quick uptake of helium, which resulted in the void filling more
than 4 times faster than the same void on an imprint made on a silicon
wafer without the porous silicon oxide layer.

Example 3

[0131]Table 5 lists PECVD process conditions for the formation of four
silicon oxide layers and a thermal oxide layer. Films were grown on DSP
3'' silicon wafers to 1.5 μm thickness in a PlasmaTherm 790. Due to
the fixed-position chuck of the PlasmaTherm 790, the silicon wafers were
placed on top of a 3.5'' diameter×0.25'' polished fused silica
plate instead of directly on the chuck in order to better approximate the
growth conditions for a 0.25'' thick fused silica template. Indentation
hardness and modulus of the PECVD silicon oxide films were measured on a
CSM Instruments NHTX nanoindentation tester with an indentor of Berkovich
geometry. PECVD silicon oxide film density was measured by X-ray
spectroscopy (XRR).

[0132]Fused silica is provided for comparison. The density was measured by
XRR. Sample 1 is 83% as dense as the non-porous fused silica, Sample 2 is
89% as dense, and Sample 3 is 96% as dense. Even with a 17% change in
relative porosity for the most porous sample, the modulus of Sample 1 was
49.6 GPa and the hardness was 4.8 GPa. Sample 1 has a ratio of Young's
modulus to relative density of (49.6/0.83)=59.8, and a refractive index
of 1.47.

Example 3

[0133]A test was developed to provide a comparison of open porosity for
different films by dispensing drops of imprint resist on a PECVD silicon
oxide surface and observing the drop diameter by optical microscope over
time to determine if the resist was penetrating the film. The films
listed in Table 6 were deposited on DSP 3'' wafers while the wafers were
spaced apart from the chuck by a 1/4'' thick polished fused silica plate.
Drops that maintained approximately the same diameter for 2 minutes (a
slight change can occur due to evaporation) were considered
"non-wicking." Various wicking rates were observed as indicated in Table
6. The wicking rates were seen to vary depending on the deposition
conditions as listed in Table 6. The filling rates were obtained from 90
nm thick imprints obtained by depositing droplets spaced 340 μm apart
on a rectangular grid in a helium-purged environment. After wicking but
before the filling test, the silicon oxide coated wafers were coated with
TranSpin® to (a) seal the open surface pores to prevent resist from
wicking in during imprinting and to (b) serve as an adhesion promoter for
the resist. Filling times are expected to decrease for highly-polished
films as an imprinting surface in comparison to films with rough
surfaces. The refractive indices of the films were measured on a J.A.
Woollam M-2000 DI ellipsometer.

[0134]Film C is porous and is intended to be coated with a cap layer for
further processing (e.g., sealing, patterning, and feature etch). This
film is an example of a layer that is suitable as a porous first layer
(e.g., a porous intermediate layer). The porosity is apparent by the
measured density, drop wicking result, and fast filling time compared to
the denser single layers listed in Table 6.

[0135]Film D includes a cap on Film C. A lower temperature cap process
(270° C.) was used which was the same temperature as the first
layer. This lower temperature process may reduce unwanted thermal changes
in the first (intermediate) layer during the second layer deposition,
because the temperature does not exceed above the first layer process.

[0136]Films B, E, F, and G were processed at 335° C. and all
demonstrate non-wicking attributes. Other process conditions (e.g., gas
flow rate, pressure, and power) were varied as noted in Table 6. A denser
cap is preferred for patterning of features into a film. Furthermore,
films E and G are formed by the same process, but film E is twice as
thick (about 8 μm) as Film G (about 4 μm). Film thicknesses were
obtained by cross-sectioning and measuring by SEM.

[0137]FIGS. 20A and 20B show photographs of wicking of an imprint resist
on Film C. The image in FIG. 20A was taken once the wafer stage was
settled after the imprint resist was deposited as drops of imprint resist
180 on Film C. The drops of imprint resist 180 penetrate the film
quickly. The outlines of the drops are no longer distinguishable in FIG.
20B, taken 5 seconds after the image in FIG. 20A. The drops 180 spread
quickly as the gases between the drops diffused through the film

[0138]FIGS. 21A and 21B show images of spreading of an imprint resist on
Film D. The image in FIG. 21A was taken once the wafer stage was settled
after the drops 180 were dispensed onto the film. FIG. 21B, taken 120
seconds later, shows substantially no change in the size of drops 180.
Film D is considered to be an example of a non-wicking film.

Example 4

[0139]A fused silica template measuring 65×65×6.4 mm was
fabricated with a PECVD porous silicon oxide film to demonstrate enhanced
gas diffusion through the template side versus the wafer side. A layer of
silicon oxide about 4 μm thick was grown on the surface of a cored-out
fused silica template having a mesa measuring 26×32 mm and 15 μm
in height. The cored-out region of the template was set on a 2''
diameter×0.25'' thick polished fused silica plate that was placed
on the chuck in a PlasmaTherm 790. After deposition of a porous silicon
oxide layer, an organic polymer and a silicon-containing polymer were
spin coated on top of the porous silicon oxide, film to planarize the
topography and cap the porous film to prevent imprint resist from
penetrating into the oxide. Spin coater CEE® 4000, available from,
Brewer Science (Rolla, Mo.), was used in the spin coating process. The
template was spin coated with 100 nm of TranSpin® and proximity baked
on a hotplate with the coated side facing down at 160° C. for 3
min. The template was then spin coated with 100 nm of a high-silicon
containing polymer resist similar to the class of materials described in
U.S. Pat. No. 7,122,079, which is incorporated herein by reference, and
proximity baked on a hotplate with the coated side facing down at
160° C. for 3 min. Because a mesa was on the template prior to
spin coating, an edge bead formed along the sides of the top surface of
the mesa, therefore a diced silicon wafer piece measuring approximately
20×20 mm was used as a mask during a dry-etch process to remove the
edge bead and to define a new mesa in the silicon oxide layer. The
silicon mask was then removed and the template was exposed to low power
oxygen plasma to oxidize the surface of the high-silicon containing
polymer to impart some SiOx character for wetting and release properties.
The template was etched and oxidized in a Oracle III etcher available
from Trion Technology (Clearwater, Fla.).

[0140]The template was imprinted in a helium purged environment on 200 mm
DSP silicon wafers coated with 60 nm of TranSpin®. MonoMat®
imprint resist, available from Molecular Imprints, Inc., was dispensed in
a rectilinear grid pattern having an approximate drop spacing of 340
μm center-to-center to produce imprints about 90 nm thick. As shown in
FIG. 22A, interstitial locations 182 between drops of imprint resist 180
were observed by a microscope camera at the time the template contacted
the resist. Images in FIGS. 22B, 22C, and 22D were taken 0.3 sec, 0.7
sec, and 1.2 sec, respectively, after the image in FIG. 22A. As seen in
FIG. 22D, the interstitial locations 182 disappeared within 1.2 seconds
after the resist was contacted by the template, such that the surface of
the template was substantially covered with imprint resist.

[0141]The photographs shown in. FIGS. 19A-19C were taken through a fused
silica template that did not contain a porous film, but was imprinted on
a similar film stack as above. FIG. 19c shows the interstitial gas pocket
remaining after 4 seconds. Thus, the porous silicon oxide layer allowed
for the quick uptake of helium, which resulted in the void filling more
than 3 times faster than a similar void with a fused silica template
which did not have a porous oxide layer.

[0142]Further modifications and alternative embodiments of various aspects
will be apparent to those skilled in the art in view of this description.
Accordingly, this description is to be construed as illustrative only. It
is to be understood that the forms shown and described herein are to be
taken as examples of embodiments. Elements and materials may be
substituted for those illustrated and described herein, parts and
processes may be reversed, and certain features may be utilized
independently, all as would be apparent to one skilled in the art after
having the benefit of this description. Changes may be made in the
elements described herein without departing from the spirit and scope as
described in the following claims.